Volcanic and anthropogenic contribution to heavy metal content in lichens from Mt. Etna and Vulcano...

Volcanic and anthropogenic contribution to heavy metal content inlichens from Mt. Etna and Vulcano island (Sicily)

D. Varrica a, A. Aiuppa a, G. DongarraÁ a,b,*aDipartimento C.F.T.A., UniversitaÁ di Palermo, via Archira® 36, 90123 Palermo, ItalybIstituto di Geochimica dei Fluidi del CNR, Via U. La Malfa 153, 90135 Palermo, Italy

Received 24 November 1998; accepted 24 August 1999

``Capsule'': Lichens were used to determine element concentrations in relation to natural or anthropogenic sources.

Abstract

Major and trace element concentrations were determined in two lichen species (Parmelia conspersa and Xanthoria calcicola) fromthe island of Vulcano and all around Mt. Etna. In both areas, the average concentrations of Al, Ca, Mg, Fe, Na, K, P and Ti aresubstantially greater than those of other elements. Several elements (Br, Pb, Sb, Au, Zn, Cu) resulted enriched with respect to the

local substrates. The Br and Pb enrichment factors turned out to be the highest among those calculated in both areas. Data indicatethat mixing between volcanic and automotive-produced particles clearly explains the range of Pb/Br shown by lichen samples. Sb isalso enriched, revealing a geogenic origin at Vulcano and a prevailing anthropic origin at Mt. Etna. Distribution maps of the

enrichment factors show a generalized enrichment of Au and Zn near Mt. Etna, whereas Cu appears to be enriched prevalently inthe NE±SE area. The highest levels of Au and Cu at Vulcano occur E±SE from the craters, following the prevailing wind direction.# 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Lichens; Trace metals; Biomonitoring; Volcanic emissions; Airborne particles

1. Introduction

Since the studies of Zoeller et al. (1974) and Duce etal. (1975), it has become clear that continental dust andsea-water spray cannot account for the global disper-sion of volatile elements (Hg, Se, Sb, As, Cu, Zn, Pb)in the atmosphere. Airborne particulate sampling inurban areas has revealed that human activities (auto-motive gasoline, oil and coal combustion, smelteractivity) produce and release to the atmosphere largeamounts of trace elements (Cawse and Peirson, 1974;Paciga et al., 1975; Harrison and Williams, 1982; Har-rison and Sturges, 1983). Volcanoes are also trace ele-ment emitters. Studies both on volcanic gases (Stoiberand Rose, 1970; Menyailov and Nikitina, 1980; Gem-mel 1987), and particulate matter collected directly

from volcanic plumes (Cadle et al., 1973; Mroz andZoeller, 1975; Lepel et al., 1978; Buat-MeÂ nard andArnold, 1978) have shown that metal elements areseparated from magma during degassing and trans-ported by rising gases as halides, native elements orsulfur compounds. Approaching the surface, they con-dense forming small particles which are then dispersedthroughout the atmosphere. Even though volcaniccontribution seems to be of little importance for mosttrace elements on a global scale (Lantzy and Mack-enzie, 1979), volcanic-derived particles may becomeimportant in areas characterized by active volcanism.For instance, Buat-MeÂ nard and Arnold (1978) showedthat particulate Cd, Hg, Se, Cu and Zn emitted bythe Mt. Etna plume are comparable to the amount ofthese elements released in the Mediterranean area byanthropogenic sources. Bergametti et al. (1984) carriedout an aircraft survey to study the chemical compositionof particulate matter in the Mt. Etna plume and itstransport in the atmosphere, and were able to identifyparticulate sulfur at a great distance (260 km) fromthe emission point. However, Bargagli et al. (1991),

0269-7491/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

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Environmental Pollution 108 (2000) 153±162

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* Corresponding author. Present address: Dipartimento C.F.T.A.,

UniversitaÁ di Palermo, via Archira® 36, 90123 Palermo, Italy. Tel.:

+39-91-6161516; fax: +39-91-6168376.

E-mail address: [email protected] (G. DongarraÁ ).

studying the metal content of vegetation on Vulcanoisland, recognized as negligible the environmentalimpact of the volcanic emission.In the present paper an attempt is made to estimate

the contribution of natural, volcanic and anthropogenicsources to metal contents in lichens from two of themost active volcanic areas in Sicily: the island of Vul-cano and Mt. Etna (Fig. 1). The spread of metals inthese two sites has also been investigated. A further aimof this paper was to evaluate whether the sole fumaroleactivity, as occurring at Vulcano island, is a signi®cantsource of metals in the surrounding environment. Thechoice to investigate the areas of Mt. Etna and Vulcanoisland arose from the consideration that they belong todi�erent geodynamic environments and exhibit sig-ni®cant di�erences in volcanic activity (permanentdegassing from open central craters and frequent highvolume lava ¯ow eruptions at Mt. Etna versus hydro-thermal±volcanic activity at Vulcano). Furthermore, theMt. Etna area is densely populated with many villagessurrounding the lower ¯anks of the volcano and a largetown (Catania) at its southeastern corner. The island ofVulcano is, on the other hand, scarcely in¯uenced by

anthropogenic activities, being devoid of industrialactivities and with a rather limited automotive tra�c.Lichen samples were collected over a large area

around both volcanic edi®ces and then analysed formajor and trace element contents. Lichens have beensuccessfully used in environmental studies concerningair quality and the atmospheric dispersion of volatilecompounds (Nieboer et al., 1972; Tuominen and Jaak-kola, 1973; Czehura, 1977; Puckett and Finegan, 1980;Garty 1985; Notcutt and Davies, 1989; Bargagli et al.,1991; Nimis et al., 1993). They are characterized by athallous structure and di�er from higher plants by hav-ing neither cuticle nor stomata and by depending on theatmosphere for their nutrition. Their peculiar physiol-ogy and morphology force them to absorb and accu-mulate from the atmosphere chemical elements ingaseous, liquid or particulate form and, owing to theabsence of excretion mechanisms, lichens cannot expelthem. The whole surface of the thallus is involved in theaccumulation process and, since it is exposed to air forlong periods of time, metal contents in lichens allow anassessment of the environmental conditions of a certainarea over prolonged periods of observation.

Fig. 1. Location of the study areas.

154 D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

2. Study sites, materials and methods

2.1. Geological settings

Mt. Etna (3300 m above sea level) is the largest activevolcano in Europe. The last considerable eruptionoccurred in 1991±93. It has grown during the last500,000 years along tensional faults cutting a thickcontinental crust. The volcanic pile is mainly composedof alkali basalt±hawaiite lava ¯ows, with more evolvedvolcanites (trachyte) and pyroclastics locally interposed(Chester et al., 1985). Etna's activity is mostly e�usiveand degassing from summit craters continuously relea-ses volatiles into the atmosphere (Allard et al., 1991).The huge amount of volatiles emitted by Mt. Etna wasexplained by Lambert et al. (1986) and Pennisi and LeCloarec (1998) by the continuous replenishing of ashallow magmatic chamber by non-degassed magmafrom depth. Up to now the most complete report onparticulate trace elements collected by air ®ltration inthe plume of Mt. Etna is that by Buat-MeÂ nard andArnold (1978), who measured concentrations of a largesuite of elements revealing high enrichment factors forS, Cl, Br, Se, Hg, Cd, Ag, Au, Zn Cu, Pb, As and Sb.Varekamp et al. (1986) found abundant Al, Fe, Ca-sulfate and sulfuric acid droplets in the volcanic plume.Cu and Zn were also found in most sulfates. Mt. Etnaaccounts for 1±10% of trace metals emitted by volca-noes on a global scale (Gauthier and Le Cloarec, 1998;Allard et al., in preparation).The island of Vulcano (Northeastern Sicily) belongs

to the volcanic arc of the Aeolian Islands. Volcanicactivity in the area started around 120,000 years ago(Keller, 1980). Recent activity (younger than 15,000years) has built up the pyroclastic and lava cone of LaFossa (Frazzetta and La Volpe, 1991). The island ismade up of rocks belonging to a shoshonitic series, frombasalt to rhyolite. More potassic undersaturated lavasare also present. The last eruption occurred in 1888±90.The present-day volcanic activity consists only of intensehydrothermal activity concentrated round the crater andin the area surrounding the cone. Literature regardingtrace elements emitted by the fumarole ®eld on Vulcanoisland is quite scanty. The sole exceptions are data fromanalyses of sublimates (Garavelli et al., 1993; Garavelli,1994) and condensates (Piccardi et al., 1979; Brondi andDall'Aglio, 1991; Pennisi et al., 1997), which usually referto only a few elements. The identi®ed minerals in sub-limates include cannizzarite (Pb46Bi54S217), galenobis-muthite (PbBi2S4), cotunite (PbCl2), sphalerite (ZnS),pyrite (FeS2), lillianite (Pb3Bi2S6) and greenockite (CdS)(Martini et al., 1988; Garavelli et al., 1993; Ferrara etal., 1995). High contents of bromine have been observedin collected salammoniac sublimates (Coradossi et al.,1996), where bromine substitutes for chlorine. Theoccurrence of Cu, Zn, Cd, Sb, Bi and Pb in condensates

has been documented by Piccardi et al. (1979), whoattributed the presence of these trace elements to thereaction of acidic solutions with the wallrock.The presence of mercury and other trace elements in

vegetation from Vulcano island and Mt. Etna wasinvestigated by Bargagli et al. (1991) and Barghigiani etal. (1988). Notcutt and Davies (1989) related the pre-sence of Cu, Fe, Mg, Mn, Zn and F in lichen samplescollected on the upper ¯anks of the volcano to thespread of the Mt. Etna plume.

2.2. Material and analytical techniques

A total of 147 lichen samples, 50 from Vulcano and97 from Mt. Etna, were collected during a 1-year survey(1997±98). The sampling sites are indicated in Figs. 4and 5. Two lichen species (Parmelia conspersa (Ehrh)Ach. and Xanthoria calcicola Ochsner), collected onrocky substrate, were used in this study. At Vulcanoisland only samples of P. conspersa were collected. AtMt. Etna 37 samples of P. conspersa were collected and60 samples of X. calcicola. Several di�erently orientatedthalli were collected from each of the 147 sampling sites.These two lichen species were chosen for sampling sincethey are widespread throughout the survey area andbecause it has been demonstrated to be in generalagreement with the chemical data from these two spe-cies (DongarraÁ et al., 1995; Carrot et al., 1996). Bothspecies belong to the `foliose' growth-form categoriesfor lichens. These lichen species can be lifted easily andalmost free from the rocky surface. Samples werealways removed from the substrate using wooden kni-ves. They were ®rst air-dried at room temperature andthen oven-dried at 40�C for 24 h. Lichens were sortedand cleaned of debris and soil with a toothbrush andsmall wooden sticks under a low magni®cation stereo-microscope. No lichen samples were found on Mt. Etnaat an altitude higher than 1800 m above sea level, andon the Vulcano crater. All the elements were analyzed atActivation Lab. Ltd (Canada), by instrumental neutronactivation analysis (INAA), except Ca, Zn, Cu, Pb, Ni,Mn, Sr, V, P, Mg, Ti and Al which were analyzed byICP±MS. NBS 1572 `citrus leaves' and 1632 B were usedas standard reference materials. Several replicates yiel-ded a precision of 20% for trace elements and in therange 5±10% for the main components. Some descrip-tive statistical parameters of major and trace elements inlichens are listed in Table 1.

2.3. Factoring method

A subset of 17 element concentrations from each stu-died area was subjected to factor analysis (principalcomponent method of factoring) examining the rela-tionship between variables (R-mode of analysis). Only afew main lithogenic constituents were introduced in the

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162 155

analysis, in order to reduce its complexity and to facil-itate interpretation of extracted factors. The number offactors to be extracted was determined by the Kaisercriterion which deletes all factors with an associatedeigenvalue of less than 1. This means to retain all factorswhich contain greater variance than the original stand-ardized variables. To bring the complexity of a variableto a minimum, the extracted factors were rotated ac-cording to the Varimax procedure, which maximizes thevariance of the squared loadings in each column. Tables2 and 3 present the terminal solutions of orthogonallyrotated factors, along with the associated eigenvaluesand communalities. These latter indicate to what extentthe factors account for the variance of each variable.

2.4. Enrichment factors

To better understand the complex data sets, enrich-ment factors (EFs) were calculated for all the elementsaccording to the following equation (Puckett and Fine-gan, 1980):

EF � �X=Al�lich:=�X=Al�subst:; �1�

where X and Al refer, respectively, to the concentrationsof the element of interest and of the reference element inthe lichen sample (lich.) and in the local substrate(subst.). Al was used as reference element as it is a well-de®ned crustal element and shows very low chemicalreactivity. An element is considered enriched when itsEF exceeds 1. Nevertheless, caution must be exercised inthe choice of the threshold value as, besides variouscontributions to metal contents in lichens, two otherfactors may increase the variance of the enrichmentfactors: experimental error in analytical determinations,and the intrinsic variance of the element/Al ratio in thesubstrate taken as reference material. The level of pos-sible analytical error was estimated at approx. 20% fortrace elements and in the range of 5±10% for the maincomponents. Considering that the relative error of ageneric quotient L=X/Y is less than or equal to the sumof relative error which a�ects each determination of Xand Y, we may assume that a reasonable estimate of theerror level in the numerator of Eq. (1) is in the 30±40%range. Uncertainty in the denominator may be moreserious, due to the large variability in trace elementcontents of rocks even of similar bulk composition. Tominimize this last type of error, average compositions ofvolcanites from Mt. Etna and Vulcano island were,respectively, computed from large sets of analysesreported in the literature (Cristofolini et al., 1991; Bar-bieri et al., 1993; Treuil et Joron, 1994; Tonarini et al.,1995, for Mt. Etna; Keller, 1980, for Vulcano island). In

Table 1

Average and variation coe�cient (CV%) of the analysed elementsa

Etna Vulcano

Average CV% Average CV%

Au 0.018 148 0.044 142

As 2 62 5 53

Br 31 58 37 46

Ca 20,668 80 17,968 63

Co 5 60 6 54

Cr 14 77 17 50

Cs 0.8 87 1.8 66

Fe 9755 74 9858 110

K 6485 48 9377 44

Mo 0.90 88 2.0 61

Na 2600 61 3525 72

Ni 8 72 7 82

Rb 20 60 36 58

Sb 1.3 130 0.6 66

Sc 3 61 4 70

Se 1.4 53 1.5 85

Sr 120 46 171 86

Th 2.2 64 5 72

U 0.6 62 1.9 60

Zn 146 107 128 34

Cu 43 100 117 109

Pb 57 95 37 87

Mn 169 67 247 76

V 29 51 36 66

P 762 55 1312 25

Mg 3423 55 3932 73

Ti 1162 48 846 61

Al 14,619 64 17,964 64

Y 7 43 14 74

a Concentrations are expressed in mg/kg (dry wt). The variation

coe�cient is the ratio: SD/mean.

Table 2

Varimax rotated factor matrix for the lichen samples from Mt. Etnaa

Factor

1

Factor

2

Factor

3

Factor

4

Communalities

Al 0.95 0.05 ÿ0.04 0.03 0.91

As 0.70 0.35 0.20 0.02 0.66

Au ÿ0.19 0.27 0.52 0.37 0.51

Br 0.27 0.75 0.14 0.04 0.66

Ca ÿ0.23 ÿ0.01 ÿ0.82 0.19 0.76

Cr 0.87 0.30 0.07 ÿ0.10 0.86

Cs 0.88 0.07 0.19 ÿ0.14 0.84

Cu 0.08 0.10 ÿ0.08 0.87 0.78

K 0.92 0.01 0.04 ÿ0.06 0.85

Na 0.74 0.29 0.02 0.31 0.74

Mg 0.91 0.20 ÿ0.01 0.08 0.88

Pb ÿ0.06 0.68 ÿ0.58 0.06 0.79

Rb 0.91 0.02 0.08 ÿ0.14 0.84

Sb 0.19 0.87 0.05 0.06 0.80

Sc 0.91 0.17 0.03 0.14 0.88

Ti 0.78 0.25 ÿ0.12 0.29 0.77

Zn 0.17 0.74 0.01 0.11 0.59

Eigenvalues 7.68 2.85 1.41 1.22

% expl. variance 0.45 0.17 0.08 0.07

Cumulative expl.

variance (%)

0.45 0.62 0.70 0.77

a For each column are also reported the associated eigenvalue,

the percentage of total variance accounted for by the factor and the

cumulative percentage.


addition, Fig. 2, showing the average EF for each ele-ment in lichens from Mt. Etna and Vulcano island,highlights two groups of elements. The ®rst, includingthe non-volatile elements (often termed lithophiles), ischaracterized by an average EF of 1.5 and a standarddeviation (s) of 0.7; the second group contains the ele-ments Br, Pb, Sb, Au, Zn and Cu, with an average EFgreater than 3, which represents the aforementionedmean value (1.5) plus 2s. Therefore, at a signi®cancelevel of 5% (a=0.05), the origin of these last elementsappears to be di�erent from the lithophile elements andthey may be considered enriched with respect to thelocal crustal source. These ®ndings are consistent withthe results of the previous multivariate analysis.An attempt is made in the following section to iden-

tify the sources of these elements and their spread inthe surrounding environment. Our approach is mainlybased on the results of factor analysis, the computedEFs and some typical element ratios.

3. Discussion

In both areas, the average concentrations of Al, Ca,Mg, Fe, Na, K, P and Ti are substantially greater thanthose of other elements. These typical crustal elementsaccount for more than 95% in weight of all the elementsanalysed. A signi®cant in¯uence of Na and Mg from the

marine environment can be ruled out on the basis of thecomputed EFs (see below).Factor analysis of the Etna data attributed 76% of

the total variance in the chemistry of the lichens to fourfactors (Table 2). The signi®cant high positive loadingsof the crustal elements Al, As, Cr, Cs, K, Na, Mg, Rb,Sc, and Ti on factor 1, which explain 44% of the totalvariance, point to the dominant contribution of soil-derived aerosols. The association of Pb, Br, Sb and Znis re¯ected on factor 2, explaining 15% of the totalvariance. These elements may be volcanic or anthropicin origin. Eight per cent of the total variance is accoun-ted for by factor 3, where Ca and Pb are present withhigh negative loadings. This factor reveals no muchadditional details other than an indication that Ca, inspite of being one of the most abundant crustal ele-ments, shows low correlations with the other lithophileelements of factor 1. The signi®cant loadings of Pb onfactors 2 and 3 also indicate two independent sourcesfor this element. The last factor is entirely dominated byCu and, subordinately, by Au. Although Na shows afactor loading on this factor as high as Au, most of itsvariance is explained by factor 1.Three factors, explaining approximately 68% of the

total variance, were extracted from Vulcano island data(Table 3). Most of the elements exhibit high factorloadings on both factors 1 and 2, making it di�cult toattribute a geochemical meaning to these factors. On theother hand, factor 3 shows the Pb±Br associationalready observed in the Etna samples, and it probablyrepresents volcanic emissions, since pollution sourcescan be ruled out to a large extent.Fig. 2 shows that the same elements are enriched at

Vulcano (Br>Pb>Sb>Zn>Au>Cu) and at Mt. Etna(Br>Pb>Sb>Zn>Au>Cs>As, Ni, Cu). The Br andPb EFs computed in this study for the lichens of Vul-cano and Etna are by far the highest among those cal-culated in both areas. They average, respectively, 72 and13 at Vulcano and 76 and 49 at Mt. Etna. One of themost important emission sources of Pb into the earth'satmosphere is the combustion of gasoline, to which Pbis added in tetra-alkyl form due to its anti-knock prop-erties. Automotive particulate also represents a signi®-cant source of bromine in the atmosphere as it is addedto gasoline to reduce the formation of Pb oxides insideautomotive engines. According to gasoline composition,the Br/Pb mass ratio in fresh automotive-producedleaded particles should be around 0.39 (Harrison andSturges, 1983; Sturges and Harrison, 1986). This ratio,termed `ethyl ratio', is generally assumed as a `marker'of aerosols produced by gasoline combustion.In the study areas, sea spray and volcanic emissions

are also potential sources of Br. Br is commonly asso-ciated with other halogens (Cl, F) in volcanic gases.Cawse (1975) explained the high Br content in air par-ticulates collected in the UK during January±March

Table 3

Varimax rotated factor matrix for the lichen samples from Vulcano

islanda

Factor 1 Factor 2 Factor 3 Communalities

Al 0.90 0.37 ÿ0.13 0.97

As 0.08 0.57 0.23 0.38

Au 0.66 ÿ0.05 0.55 0.73

Br 0.10 0.04 0.64 0.42

Ca 0.17 0.72 0.03 0.55

Cr 0.58 0.64 0.17 0.78

Cs 0.91 ÿ0.12 ÿ0.04 0.84

Cu ÿ0.03 0.72 ÿ0.39 0.68

K 0.94 ÿ0.02 ÿ0.04 0.89

Na 0.91 0.24 0.02 0.88

Mg 0.78 0.51 ÿ0.16 0.89

Pb 0.01 0.13 0.70 0.51

Rb 0.86 ÿ0.06 0.19 0.78

Sb ÿ0.23 0.01 0.37 0.19

Sc 0.54 0.74 ÿ0.10 0.86

Ti 0.83 0.36 ÿ0.10 0.83

Zn ÿ0.14 0.50 0.19 0.31

Eingevalues 6.55 3.20 1.71

% expl. variance 0.39 0.19 0.10

Cumulative expl.

variance (%)

0.39 0.58 0.68

a For each column are also reported the associated eigenvalue,

the percentage of total variance accounted for by the factor and the

cumulative percentage.


1973 as partly due to particles emitted during the erup-tion of Heimaey volcano in Iceland. Buat-MeÂ nard andArnold (1978) estimate a Br ¯ux of 3200 t/year and a Pb¯ux of 130 t/year from Mt. Etna. Estimated ¯uxes forVulcano (0.078 t/year for Br and 0.01 t/year for Pb,respectively) are considerably lower (Martini et al.,1988). A correction for sea spray contribution has beenapplied to our data by the following equation:

Br� � Brtot ÿ �Br=Na�sea �Nalich �2�

However, the calculated Br non-marine concentration(Br*) is underestimated because the previous equationassumes that all the sodium in lichen samples comesfrom sea water.Fig. 3 is a plot of Pb/Br* ratios versus Pb absolute

concentrations in the analysed lichens. Many samplepoints cluster close to the ethyl ratio (here as Pb/Br=2.7) suggesting that deposition of automotive parti-cles is a process occurring in both areas. However, verylow ratios are also observed. The range of variability forthe Pb/Br ratio in some volcanic ¯uids is also plotted inFig. 3, for comparative purposes. Buat-Menard andArnold (1978) give a Pb/Br ratio of 0.057 for the parti-cles collected from the Etna plume. The values (from 0.3to 0.57) measured by the same authors in particulatematter collected near high-temperature manifestations(hornitos and hot vents) are similar to those shown bygases released by other volcanoes (Stoiber and Rose,1970; Gemmel, 1987). Fig. 3 clearly indicates that mix-ing between volcanic particles and automotive-produced

particles explains the range of Pb/Br shown by lichensamples. Distribution maps of the Pb/Br* ratio areshown in Fig. 4. At Mt. Etna, the anthropogenic

Fig. 2. Average enrichment factors (EFs) for the analysed elements in lichen samples from Mt. Etna and Vulcano island. EFs have been calculated

using Al as the reference element and average concentrations in local rocks taken from the literature. The dashed line indicates the boundary, at a

signi®cance level of 5% (a=0.05), between enriched and non-enriched elements.

Fig. 3. Pb/Br* ratio versus total Pb (ppm) in lichen samples from Mt.

Etna and Vulcano island. Br* is the Br concentration after correction

for sea water contribution. The ethyl ratio (Pb/Br=2.7) and the

observed range in earth's volcanic ¯uids are also shown.


contribution is more signi®cant near the town of Cata-nia and along the main roads. Lowest Pb/Br* ratiosare observed on the highest slopes of the volcano.At Vulcano, the highest Pb/Br* ratios are observed inthe lichen samples collected along a road connecting thevillage with the inner part of the island.After Br and Pb, Sb is by far the most enriched ele-

ment found at Vulcano and Mt. Etna. Average EFs forSb are considerably higher at Mt. Etna (EF=37) thanat Vulcano (EF=9). As indicated by factor analysis, Sbis mainly correlated with Pb and Br in both areas. Whileat Vulcano island Sb seems to have mainly a geogenicorigin, the high EFs of Sb at Mt. Etna are mainly due toanthropogenic sources as the observed Pb/Sb ratio inlichens is in the same range (20±40) found in aerosolsamples collected in urban areas of Sicily (Aiuppa et al.,in preparation) and in other towns (Bonanni et al., 1992).Among the most common elements present in volca-

nic plumes and high-temperature fumaroles are Au, Cuand Zn (Lepel et al., 1978; Symonds et al., 1987; Gem-mel, 1987; Zreda-Gostynska et al., 1997). Table 1 indi-cates the general higher contents of Au and Cu inlichens from Vulcano island than from Mt. Etna. Dis-tribution maps of the EFs of Au, Cu and Zn are shownin Fig. 5. Generalized enrichment of Au and Zn may berecognized in the Etnean area, probably because theyare in¯uenced both by natural and anthropogenic sour-ces, while Cu is mainly enriched in the NE±SE area.With regard to the latter element, a very high EF (356)was obtained by Vie le Sage (1983) from a hornito at400�C, situated along the southeast crater of Mt. Etna.

Notcutt and Davies (1989) showed that high con-centrations of copper in lichens may be recognized eastand northeast of the main craters and related such ananomaly, as well as the presence of ¯uorine, to thespread of plume in the wake of prevailing winds.With respect to the island of Vulcano, it may be

observed that Zn is enriched over the whole survey areaand, particularly, in the eastern part. Similarly, thehighest levels of Au and Cu occur E±SE of the crater,following the prevailing wind direction on the island.Signi®cant anomalies of Cu and Zn were also observedby Bargagli et al. (1991) in surface soils and pine needlesfrom Vulcano. Resuspension of dust from outcroppinghydrothermal deposits, enriched in Cu, Zn and Au(Fulignati and Sbrana, 1998), cannot be ruled out.Finally, the Ca±Pb association, as indicated by factor

analysis of Mt. Etna data, suggests that automobile fuelcombustion may produce the slight EF of Ca (EF=3).Silva and Prather (1997) have shown that 60% of theinorganic particles produced by old vehicles are char-acterized by the chemical association Pb±Ca. Ca isbelieved to be a remnant of the re®ning process, as itis contained to a large extent in crude oil. Industrialactivities near Mt. Etna may also explain the slightenrichment observed for Ni (average EF=3).

4. Conclusions

Two di�erent groups of elements have been recog-nized in the analyzed lichens: the lithophile elements,

Fig. 4. Distribution maps of Pb/Br* at Mt. Etna and Vulcano island. Br* is the Br concentration after correction for sea water contribution.


Fig. 5. Distribution maps of Au, Cu and Zn enrichment factors (EFs) for (a) Vulcano island and (b) Mt. Etna.


derived from the local crustal material, and the enrichedelements (Sb, Br, Pb, Zn, Au, Cu), forming volatilecompounds and mainly originating from anthropogenicsources and/or volcanic gases. Among the latter, Pb, Brand Sb concentrations in lichens seem to be con-siderably a�ected by human activities. However, theEFs observed for Pb and Br in lichens cannot be attrib-uted exclusively to automotive fuel combustion, but arepartly the result of volcanic exhalations. This is moreevident on the island of Vulcano, where the anthro-pogenic in¯uence is very limited. The di�usion of Br issurprising since, apart from any marine contribution, itoccurs in the air at very great distances from possiblesources of emission. From an environmental viewpointthis presents a particularly important problem concern-ing the background levels in air currently reached by Br.Cu, Au and Zn contents are mainly derived from vol-canic degassing. It appears from this study that theirdispersion is related to distance from craters as well asthe prevailing wind direction.Comparison between the chemical data reported in

the literature and those obtained during the presentresearch, provided in a manner completely independentof other conventional methods, con®rms that volcanoesare a continuous source of trace elements injected intothe atmosphere: erroneously, it is believed that they areonly responsible for the emission of metals and otherelements during eruptive phases. Fumarole activity, asthe data regarding the island of Vulcano suggest, maybe a signi®cant source of metals in the surroundingenvironment. In towns and cities near volcanic areas,natural emissions are added to those due to anthropo-genic activity. Therefore, both geogenic and anthro-pogenic sources must be taken into account whenplanning environmental controls.The results obtained in this work show that a sig-

ni®cant part of the atmospheric aerosol deposited onlichens derives from weathering of rocks and fromtransport of the ®nest material by winds. Although thiscircumstance may constitute a disadvantage in usinglichens, as soil contribution may obscure the e�ects ofdi�erent metal sources, they still remain useful, simpleand cheap sampling media for mapping the dispersal ofsome environmental contaminants.

Acknowledgements

The authors would like to thank two anonymousreviewers who signi®cantly improved the quality of thispaper by their insightful comments. This research wassupported by the Italian National Council of Research(CNR) - Istituto di Geochimica dei Fluidi, which theauthors whish to thank. Financial support was alsoprovided by MURST (funds 60%).

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